Electron tube gettering means



June 5, 1956 G. J. AGULE 2,749,466

ELECTRON TUBE GETTERING MEANS Filed Dec. 18, 1951 I I 31 36 2 fl 60 I 65 d! 65 37 Qf 2a 35 1 INVENTOR GEORGE J. AGULE United States Patent ELECTRON TUBE GETTERING MEANS George J. Agule, Stamford, Conn, assignor to Macblett Laboratories, Incorporated, Springdalc, Come, a corporation of Connecticut Application December 18, 1951, Serial No. 262,275

2 Claims. (Cl. 313-180) This invention concerns a novel gettering means for use within a vacuum envelope wherein the gettering substance may be activated at any time during the storage or during the use of the tube.

Even the most thorough outgassing of electron tubes fails to remove all of the gases occluded and included within metal parts. Furthermore, despite extensive baking and other precautions taken to insure complete exhaust, gas molecules adhere to the inner surfaces of a tubes vacuum envelope. For these reasons, an unused tube will eventually become gassy as the gases slowly leak off tube parts. Also, when the tube is being used, various erratic conditions, such as flash arcs, may be responsible for the release of large quantities of gases.

Tubes stored for long periods of time periodically require a so-called clean-up of the gases which have leaked off tube parts in order to prevent the gases from reaching a prohibitive level. The periodic clean up is frequently accomplished by a heat-activated getter. Often, heatactivation of a getter involves placing the storage tube in a socket and operating the tube for some time. Placing the tube in the socket requires extensive handling which increases the opportunity for breakage of the tubes relatively fragile filament. Furthermore, it is frequently necessary to remove a tube in service in order to free a socket for use by a storage tube. Removal of the tube in use necessitates the handling of that tube as well as the storage tube. Much damage and inconvenience had been occasioned by such handling of tubes incident to gettering storage tubes.

My invention eliminates the necessity of handling the tubes in order to activate their getters. The gettering means of my invention permits activation of the getter by merely applying a predetermined voltage across a pair of getter terminals outside the tube envelope. These getter terminals are coaxial and are located at one end of the tube structure where they are easily accessible. Thus, activation of the getter of a stored tube may even be accomplished in its place of storage, frequently without moving the tube. Likewise, the getter terminals may be conveniently reached even when a tube is employed with cavity circuitry. By the same token, this arrangement of getter terminals permits the getter and its associated circuitry to be located in a region where they will not interfere with the high frequency structural design of a tube.

My getter may be activated without operating the tube or even energizing the filament. By the same token, when the tube is in service, the getter need not be activated unless it is needed. Such controlled activation of the getter is made possible by connecting one end of the getter, or its heater element, to a terminal which has no other function than to act as a getter terminal. Unless this terminal is used to complete an activating circuit through the getter or its heater, the getter will remain inactive. The other getter terminal may be a filament terminal or a terminal for any other electrode. The

2,749,466 "Patented June 5, 1956 terminal used exclusively for gettering purposes is preferably the inner terminal.

My gettering means permits the gettering substance to be placed in a location remote from the cathode, or other parts of the tube which become severely heated. The gettering substance may be activated only upon application of voltage to the getter terminals since the gettering substance is completely removed from the high temperature encountered in certain localities within the vacuum -envelope. Even when a tube employing my gettering means is heated during the outgassing processing of manufacture, the temperature of the gettering substance remains substantially below that temperature at which it tends to absorb gases. As a consequence, all of the occluded gases driven off during the processing of the tube maybe evacuated by pumping, and the gettering substance left uncontaminated and free to absorb its capacity of gases at subsequent times.

For a better understanding of my invention reference is made to the drawing which illustrates in section a tube employing my novel gettering means.

In the electron tube illustrated a cylindrical coaxial arrangement of the electrodes is employed. Anode 10, which is a heavy walled copper cup, contains the grid structure which is composed of circularly arranged parallel struts 11 around which the active grid wire 12 is helically wrapped. The grid is terminated at that end remote from its support in cap member 13 which lends rigidity to the structure. Coaxially within the grid structure is the filament. The filament is composed of a plurality of parallel strands 14 having convergent portions at that end remote from the filament supports, said convergent portions being terminated in parallel portions adjacent the axis which are advantageously bound together by fine wire 15 and welded in place.

The anode cup 10 forms a part of the vacuum envelope. Attached to the lip of this cup is tubular member 17 which, in effect, is folded back from the lip to which it is aflixed over the cup side walls. Member 17 is terminated in heavy annular terminal 18, part of which also serves as a portion of the vacuum envelope.

The grid structure is terminated at its supported end in a ring 20 which is fastened to heavy annular metallic terminal member 21 against a flat surface by means of screws 22.

The grid terminal 21 and the anode terminal 18 are separated by a coltunn wherein tubular metallic members 23 and 24 are sealed together by means of a large glass ring 25'. Tubular member 23 is sealed directly to terminal member 18. Rather than sealing tubular member 24 directly to terminal member 21, however, a tubular member 26 is interposed and is sealed to member 21. Radially extending flanges 24a and 26a, of members 24 and 26 respectively, may be sealed together using high frequency heating to melt hard solder as described in my U. S. patent application Serial No. 118,878, filed September 30, 1949, now Pat. No. 2,654,822. This is advantageously made the final seal in constructing the tube.

The filament strands 14 are connected to support rods 28 by means of radially extending metallic tabs 29. Alternate support rods are, in turn, terminatedin annular member 30 which is, in effect, an inward extending flange of tubular member 31. The other strands pass through holes in annular member 30 and are terminated in tubular member 32. Annular members 33 and 34-, which are connected respectively to tubular members 31 and 32, provide cathode terminals for use with my filament. Cathode terminal 3 is joined to grid terminal 21 by means of a column composed of tubular metallic members 35 and 36 sealed to glass ring 37. Cathode terminals 3.3 and 34 are likewise connected by a column composed of tubular member 38 and 39 connected by glass ring 40. These various columns and terminal members all provide part of the vacuum envelope of my tube structure. If the cathode terminal 34 were made disk-like rather than annular, as shown, the resulting structure would be essentially that described in my copending application Serial No. 185,645, filed September 19, 1950, now Pat No. 2,707,757.

The Water jacket shown is essentially the one which is described in the copending application, Serial No. 25 8,926 of Raymond H. Rheaume, filed November 29, 1951, now Pat. No. 2,693,347. This water jacket consists of a tubular bafiie member 42 which is separated from the anode cup 10 and evenly spaced therefrom by a plurality of spiral wires 43 which extend between the anode and the baffle and act as walls for directing the flow of the coolant in channels between the walls. Allixed to one end of the baffie member 42 is a trough-like member which has a radially inward extending portion 44 attached to a battle member 42, a tubular portion 45 at the inner end thereof, a radially extending portion 46 at the opposite end of the tube, a tubular member 47 at the outer edge of member 46 extending upward toward the baflle member and a small flange 48 extending outward at the end of tubular member 47 adjacent the bafiie. To the outer edge of flange 48 is attached tubular member 49 which, in turn, is connected to anode portion 17, previously described. An exhaust tubulation may be conveniently provided through the bottom of the cup-like anode on the axis of the tube, which tubulation will be protected by its location within tubular member 45. The space within tubular member 45 also provides a means of access for the coolant to enter the space between the anode 10 and battle member 4-2. The coolant proceeds upward toward the joint between the anode cup and anode member 17 and thence is free to pass downward between member 17 and the bafile to the space between member 49 and the baflle; whence it will pass into the annular trough formed by members 45, 46 and 47. A plurality of holes 52 through member 46 permits the escape of the coolant. The tube may be held in place above a source of coolant by means of radially outward extending pins 53 which are alfixed in member 47 and which fit into means in a socket for receiving and holding the pins in place.

My invention is directed primarily to a gettering structure for use in this tube. As shown, an additional coaxial terminal 55, which in this instance is circular in shape, is affixed to cathode terminal 34 by means of a column composed of tubular members 56 and 57 separated by insulating ring 58. An axial rod 59 extends into the vacuum envelope from terminal 55. To the end of this axial rod is affixed a helical coil of gettering material, i. e., material which, when sufiiciently heated, will absorb or adsorb gases. The gettering material is conveniently located within tubular cathode support member 32. The helical coil is wrapped around the rod 59 as an axis and is advantageously terminated at some point before cathode terminal 34. It is thereafter affixed to red 61 which parallels rod 5i but which is affixed to member 62, effectively an inwardly extending flange of tubular filament support 32. The wire of gettering material may be of zirconium or any other gettering material capable of formation into the shape of a relatively high resistance wire. It may be atlixed to its support wires or rods by binding with fine refractory wire and thereafter welding it in place. Planar member 63, which is atfixed to member 62 by screws 64 or similar means, is here provided as a heat shield. Access to the getter is afforded various gases which may be present within the vacuum envelope by openings 65 through member 31 and openings 66 through member 32.

My gettering means is easily mounted in the tube end structure assembly. The end structure assembly is formed by sealing together with the insulating rings the tubular column members aflixed to each terminal. Prior to sealing together, there are completed the various sub-assemblies consisting of the grid, filament, filament-getter and getter terminals, the respective element support structures atlixed to each terminal and the tubular column members affixed to each terminal. For instance, the getter terminal assembly includes the getter support rod 59 afiixed to terminal 55. Upon assembly, the tube end structure has rod 59 extending into the envelope within tubular filament support 32. A sub-assembly consisting of rod conductor 61 and helical getter wire 60, wherein one end of the getter wire is allixed to one end of the rod conductor, as previously described, is then introduced into the end structure assembly. The junction of the rod conductor 61 and the getter 60 is introduced first through the open, unattached end of tubular filament support 32. The helical getter wire is arranged to surround the axial rod conductor 59. Thereafter, the unattached end of the getter wire 60 is spot-welded to the end of axial conductor rod 59 and the rod conductor 61 is affixed to the annular collar 62. This getter construction is structurally strong.

The operation of this gettering arrangement is extremely simple. Whenever it is desired to activate the getter, a predetermined voltage which will produce a current sutfieient to raise the temperature of the gettering substance to its active level is placed across the terminals 34 and 55. If the getter is designed for such operation, it may be activated merely by connecting the getter terminal 55 and the filament terminal 33. Thus, the filament and the getter will be effectively connected in parallel.

It is apparent that the getter need be used only when desired. It may be used before the tube is put into operation, or it may be used while the tube is in operation. However, it need not be used while the tube is in operation. it is of particular advantage to have a getter of this type when thoriated tungsten filament strands are employed. Thoriated tungsten, which is frequently used to obtain increased emission efiiciency, is particularly susceptible to poisoning. Poisoning occurs as the thorium at the filament surface combines with the gases which are released Within the tube. Such depletion of the thorium at the filament surface necessitates reactivation of the filament, by which process additional thorium is brought to the filament surface. Repeated reactivation of the filament will exhaust the supply of thoria. With my invention it is possible to absorb the gases present in a tube which has had a long period of storage before the tube is operated. Thus, poisoning of the filament is avoided.

As pointed out previously, the fact that the getter is within a portion of the envelope which is not severely heated and that it is shielded by its location relative to the support and shielding members is of advantage in avoiding activation of the getter during manufacture and during other periods when such activation is undesirable or unnecessary.

The structure shown is not the only form in which my invention may be employed. Gettering materials other than zirconium may be employed. Likewise, the form of the getter substance employed may be difierent. For instance, the gettering substance may be in powdered form applied to a surface which may be conveniently heated by a heater which is connected to gettering terminals like those shown or to some other arrangement of terminals within the scope of the claims. Thus broadly speaking, my invention permits the use of a gettering substance which is either directly heated by the generation of heat due to its internal resistance to the flow of current or indirectly heated by a separate heater element. in either event a heater element is employed, but in the former case the heater and the gettering substance are one.

I claim:

1. An electron discharge device comprising an evacuated envelope containing a filament, an anode and a gettering substance, a heater element for the gettering substance, a plurality of coaxial terminals which have contact surfaces outside the vacuum envelope, a tubular member projecting into the vacuum envelope and surrounding the heater and the gettering substance except for openings which provide access to the getter, leads connecting the heater between the two innermost terminals and a heat shield located between the filament and the getter and closing the inner end of the tubular member.

2. An electron discharge device comprising an evacuated envelope containing a filament, an anode and a gettering substance, a heater element for the gettering substance, a plurality of coaxial terminals which have contact surfaces outside the vacuum envelope, the outer terminal of which serves also as a filament terminal, a tubular filament lead connected to the filament terminal and surrounding the heater and the gettering substance except for openings which provide access to the getter, leads connecting the heater between the two innermost terminals and a heat shield located between the filament and the getter and closing the inner end of the tubular member.

References Cited in the file of this patent UNITED STATES PATENTS 

